The pictures then ended up being posted on Instagram around Father’s Day last year by the investment banker’s daughter, but only revealed in a national newspaper early this month. Mr Cullinan's daughter had uploaded the photos with the message: “Happy Father’s Day to the indisputable king of Snapchat.”

Mr Cullinan drew heavy criticism for not taking his role seriously, with opponents highlighting that RBS remains majority Government-owned. He will now leave the bank after more than six years.

He said on Monday that he was "pleased and proud to have played a significant part in restoring RBS to a safe and sound agenda". He wished all his colleagues continued success.

Last month analysts described Mr Cullinan as "phenomenal", remarking that it was not a surprise that he had been given more responsibility by Mr McEwan on the back of "his experience and what he's delivered".

RBS said that Chris Marks and Mark Bailie would join the bank's executive committee as joint CEOs of corporate and institutional banking, in Mr Cullinan's place.